Tone generator



P 1964 R. J. ZIEHLKE 3,150,227

TONE GENERATOR Filed June 9, 1961 5 Sheets-Sheet l 2% Tan/A g GENEP/OTbR'S P 22, 1964 R. J. ZIEHLKE 3,150,227

TONE GENERATOR June 9, 5 sheets sheet 2 .zaewifz'el ge Sept. 22, 1964 R. J. ZIEHLKE 3,150,227

TONE GENERATOR Filed June 9, 1961 5 Sheets-Sheet 3 WW W AIM

p 2, 1964 R. J. ZIEHLKE 3,150,227

TONE GENERATOR Filed June 9, 1961 5 Sheets-Sheet 4 Sept. 22, 1964 R. J. ZIEHLKE 3,150|227 TONE GENERATOR Filed June 9, 1961 s Sheets-Sheet s United States Patent 3,150,227 TGNE GENERATOR Robert .l. Ziehlke, lanesville, Wis, assignor to Gibbs Manufacturing 8: Research Corporation, Janesville, Wis, a corporation of Wisconsin Filed June 9, 1961, Ser. No. 116,924 21 Claims. (Cl. 84-118) This invention relates to improvements in musical tone generators of the photoelectric type.

This application is a continuation in part of the copending United States patent application of Robert J. Ziehlke, Serial No. 753,771, filed August 7, 1958, entitled Tone Generator.

The photoelectric scanning method for producing tone signals has for many years intrigued those working in the musical instrument art and innumerable attempts have been made to make a commercially feasible electric organ utilizing these principles. However, the complex problems involved in this approach have been so great that no truly successful commercial photoelectric organ has been devised which can compete with other organs of comparable quality utilizing other electrical and electronic approaches.

There are many reasons for the continued failure to commercialize this type of organ. In some cases the problem is that the cost is too great in relation to the results obtained for the organ to successfully compete on the market. In other cases where attempts have been made to reduce cost, it has not been possible to produce an organ with a quality which is comparable with that of other organs in a similar price range. So far as is known, applicants invention, with minor alternatives dictated by manufacturing techniques, is the first truly competitive organ on the market which utilizes photoelectric principles for generating the tones. Not only does the organ compete favorably in price, but as will appear, it also has certain inherent tonal advantages.

Accordingly, it is a primary object of the present invention to provide an improved electric organ, the tone signals of which are produced by photoelectric Scanning means.

In the photoelectric organ of the present invention, the first step in determining a means of producing a truly competitive quality organ was the selection in the interest of economy of a scheme using a single photocell for receiving and reproducing all of the signals corresponding to a group of octavely related tones of differing tone qualities. Another step in the process of selection was the determination of a commercially feasible means for keying the various tones and for providing a suitable scanning means. It was known that several attempts had been made in the past to design a satisfactory structure including a mask with tone pattern openings and a cooperating rotatable disc with scanning slots to produce the desired tone signals in the form of light energy and to project the signals in light form upon a photocell. This arrangement with individually keyed light bulbs for each tone has theoretical advantages. However, so far as is known, all prior attempts to build such an organ failed to produce tones of satisfactory quality as compared with other organs of similar cost. Nevertheless, this general approach was adopted, since it has great promise, providing that the extremely difficult problems can be solved.

One of the basic problems has to do with tone intensity equalization. Since each of the light signals for the tones applied either singly or jointly to the photocell produces a signal amplitude in the photocell which is a function of the light intensity, the light intensities for the various notes should be adjusted to achieve a satisfactory relative level. It is readily apparent that once the mixed tone signals are formed electrically by the photocell, little can 3,156,227. Patented Sept. 22, 1964 be done to vary the relative amplitudes of the harmonic components of even a single tone, much less the mixed frequencies of several tones played simultaneously.

It was recognized that serious space limitations prevail and that the mechanism selected must lend itself to mass production manufacturing techniques. A tone generator of octavely related tones is required for each note (12) in an octave. Since one lamp is provided for each tone to be produced by the generator, all of the lamps and tone masks had to be placed within the usable area of the mask discs.

A mask with suitable wave pattern openings of sufficient accuracy was then produced and means were provided for assuring the very uniform illumination of all parts of each mask opening. Next, special attention was given to the slot arrangement in the scanning disc, since the scanning of the wave forms is all important in producing the desired intensity levels for the various harmonic components which are incorporated in wave pattern openings. The amplitude of the signals produced by the photocell in response to the scanned light was found to be a function of the rate of change of scanned light as well as a function of the light intensity. By consideration of these and other problems and the use of new scanning slot and mask techniques, very satisfactory tone reproduction was achieved.

In the preparation of the mask and scanning disc, the mask openings and the scanning slots are arranged in opposed concentric rows; and the arcuate distance between scanning slot centers in each row (the slot pitch) is equal to the arcuate length of the mask openings in the corresponding row. In order to provide succeedingly higher octaves from row to row, the number of scanning slots in each row outwardly is doubled and the mask opening arcuate lengths are divided by two. However, this known approach, unless considerably modified, provides completely unsatisfactory results, because neither acceptable relative tone intensities nor relative harmonic content amplitudes in the tones are achieved.

As one proceeds from row to row the pattern openings are divided by two, but the number of scanning slots is multiplied by two; hence, the slots would admit twice as much light in a given time interval were it not that the mask pattern is one-half as wide. But the slot widths are also one-half as wide, and this would appear to reduce the amount of light per interval by one-half. It was found that the light per interval was not so reduced however, due perhaps to the efficiency of the system at higher speeds and the clarity of the transparent portion of the slots and mask patterns of small dimensions.

It was then found, however, that by maintaining the ratio of the mask opening length to the slot width at a value higher than the number of the highest significant harmonic to be reproduced, for example in the order of 12: 1, faithful reproduction of the desired higher harmonics of the mask openings could be readily achieved. Hence, it appeared that substantially improved results could be obtained by using slot widths which are divided by two in each succeeding outer row, thus maintaining a constant mask opening length to slot width ratio.

However, this proved to be commercially impracticable without further modification. Because of space limitations in the outer rows where typically there may be 288 and 576 lines, the lines become extremely narrow. This causes a poor signal-to-noise ratio and an unacceptably low signal level for the higher pitch tones. Enough light must pass to produced signals substantially higher than the normal noise level of the photocell and the light itself must have a low noise level.

It was found that the signal-to-noise ratios and the relative intensities of the tones could be substantially improved and the faithful reproduction of desired harmonic content maintained by making each wave pattern opening symmetrical from either side of a central circumferential line to increase the radial dimension of the opening and, where mechanically feasible, by increasing the radial dimensions of the wave pattern openings as the slot width decreases to provide a more constant light intensity for the same tone quality from octave to octave. The practical radial dimension available to the pattern openings in each row is of course limited, and therefore the highest octaves are still lacking in sufiicient signal strength although the intermediate octaves are completely or largely signal amplitude equalized.

By the expedient of providing two or more identical openings of appropriate size for each tone in the higher octaves and simultaneously scanning the openings, faithful reproduction of the fundamental and harmonics of the tone qualities at desired amplitude levels can be achieved without appreciable distortion and with advantageous signal-toenoise ratios.

Even with the best photographic reproduction techniques available, the forming of 288 or 576 slots with the slot wodths being one-twelfth the distance between slot centers is difiicult without encountering a slight amount of noise. The radial slot edges are necessarily somewhat irregular, even with the best manufacturing techniques, thereby producing noise; and when the slot width is unusually small, these irregular edges account for a greater ratio of the total light. passed by 'the slot. This problem was largely solved by determining the extent to which the higher harmonics could be eliminated from the tone qualities because they approach inaudibility and by making the slots in the outer circles somewhat wider, thus preserving the desired fundamentals and harmonics and eliminating those in the inaudible and near inaudible range. Thisarrangement increases thelight passed by the slots in the outer rows and additionally makes the formation of these slots less critical. Thus the slots for scanning the tone patterns in the higher-octaves were. assigned lower pattern opening widthto slot width ratios with no detrimental eifectupon the quality of the tones produced by the organ and atthe same time providing the desired amplitude equalization which was so important for retaining the true'harmonic content of each wave form and the desired amplitude equalization for the various octavely related tones.

Accordingly, it is a primary object of the present invention to provide an improved method and means in a photoelectric organ for producing musical tone signals with the desired relative fundamental and harmonic amplitudes and for producing octavely related tones with a desired degree of amplitude equalization.

Although these techniques for producing a truly satis factory commercial organ of the photoelectric type are particularly advantageous where a single photosensitive device is utilized to generate all of the octavely related tones, nevertheless it will be appreciated that they are also advantageous and lend appreciable economy advantages in otherwise similar apparatus which may have more than one photosensitive device for picking up signals from the various tone pattern openings. .It can be seen that,

in such an embodiment with several photosensitive devices, individual amplification of the various octavely' related tones is not required and that the mcans used to produce these improved results are provided at no additional cost. The improved mask and scanning disc are readily reproduceable at the same cost as masks and scanning discs which are generally similar but which do not include the novel features which provide for successful operation of the photoelectric tone" generating and keying system to be described in greater detail presently.

A feature of theinvention is the provision of a tone generator including a mask plate having a plurality of light transmitting tone representing areas or openings, a plurality of selectively actuable light sources, one associated with each of the mask plate areas, a scanning plate s having light transmitting scanning slots for scanning the light from the mask areas, light sensitive means for converting scanned light to an electrical signal, means for moving the scanning plate with respect to the mask plate and means for actuating the light sources. A further feature is that the mask and scanning plates are of transparent material with opaque mask and scanning coatings on one surface thereof, and they are mounted with the coated surfaces closely adjacent each other.

Yet another feature is theprovision of a tone generator including a light source, a mask having a light transmitting area, the longitudinal edges of which have a configuration representing the harmonic makeup of=a musical tone, scanning means having scanning areas spaced apart a distance equal to the longitudinal extent of the mask area, and means for converting the scanned light into an electrical signal. Still a further feature is that the trans Verse or radial dimension of the scanning areas represents the amplitude of the tone.

Yet another feature is that the mask has a plurality of tone representing areas arranged in generally circular rows, and the scanning plate is provided with scanning slots arranged in similar rows, with more slots in each row than in the next inner row. Yet a further feature is that the number of scanning slots in each succeeding row is an integral multiple of the number of slots in the next inner row. I

Another feature 'is that the mask is provided with a plurality of identical note representing areas and the asso ciated scanning slots are spaced apart a distance greater than the longitudinal extent of the-individualpattern, to provide frequency multiplication. And a further feature is that the ratio of width to pitch of the scanning slots is less in the inner rows than in the outer, tending to equalize the amplitude of the generated tones.

Further features and advantages of the invention will readily be apparent from the following specification and from the drawings, in which:

FIG. 1 is a block diagram of an electronic organ which may utilize the invention;

FIG. 2 is a diagrammatic section of a tonegenerator embodying the invention; 7

FIG. 3 is a fragmentary exploded view of a'portion of a mask andscanning plate;

FIG. 4 is an enlarged vertical section taken generally through line 4-4 in FIG. 5 to illustrate the tone generator embodying the invention;

FIG. 5 is an'elevation of a tone generator mounting panel illustrating the layout of the driving arrangement for thescanning discs;

FIG. 6 is a plan View of a scanning disc;

FIG. 7 is a plan view of a mask; and

FIGS. 8-13 are a series of enlarged fragmentary views illustrating in superposed relation the note representing mask areas and the scanning slots for various notes.

The tone representing areas of the mask of the tone generator disclosed herein represent the tones of actual organ pipes, and preferably include all of the significant harmonics of the original note in their proper amplitude relation. The tones produced by the generator are effectively replicas of the-tones of the pipe organ and much more realistic than tones produced by electronic oscillator and filter networks of any practical design. Ina musical instrument incorporating tone generators of this invention of a keyboard, through stop selector 19, which determines the particular tone qualities that are generated when a key is depressed, as will appear in more detail below.

In a preferred embodiment of the invention, one tone generator is provided for each note in an octave, with each generator being capable of producing signals representing the various tonal qualities of the stops with which the instrument is provided. the standard musical scale there are twelve tone generators, each of which generates one note, as A, for each octave and each of the stops, or tonal qualities, of the instrument.

Turning now to FIGS. 2 and 3, the basic tone generating principle of the instrument is illustrated. A mask 2t) has formed thereon a light transmitting area 21, repr senting a particular tone quality. A scanning member 22 is provided with scanning slots 23 which move past the tone representing area 21. A lamp 24 provides light which is collimated by lens 25 so that the tone representing area 21 is uniformly illuminated. As the scanning member 22 moves past mask 20, the light passing through tone representing area 21 is scanned by slots 23, and impinges on photosensitive device 26, which converts the scanned light variations to electrical variations appearing at terminals 27.

The tonal quality or harmonic content of the reproduced tone is determined by the lateral configuration of the mask area, that is the configuration at right angles to the direction of movement of the scanning slots. The frequency is determined by the speed at which the light passing through the mask is scanned. In determining the mask configuration, the particular tone, as from an organ pipe, is analyzed to determine its harmonic make up. This information is then utilized to plot the mask area configuration, with due regard to the sensitivity of the photocell 26, amplitude equalization of octavely related tone qualities, and the other elements of the system, to the various frequencies involved.

Turning now to FIG. 4, a physical embodiment of a tone generator incorporating the invention is shown. A block member of slightly resilient, composition material is mounted on spacers 31 secured to support plate 32. The block 30 has a plurality of holes or apertures 33 extending therethrough, which receive lamps 35 mounted on a supporting board 34. Preferably the lamps 35 are energized through a circuit (not shown) printed on the supporting board, and connected through the stop selector 19 with keys 18.

A mask plate 36 is fitted to the surface of block 30 opposite circuit board 34. The mask plate is of a transparent material, as a clear plastic, and has applied to the outer surface thereof an opaque coating 37, in which are formed note representing openings or areas 38, which permit the transmission of light in a desired pattern, as will appear more fully later. The undersurface of mask plate 36 has light collimating lenses 39 formed integrally therewith, which extend into the holes 33 in block 30 insuring that light from lamps 35 travels through mask plate 36 in a direction normal to the surface thereof and illuminates the note representing areas uniformly.

A rotatable scanning plate or disc 46 is mounted on a shaft 41 by means of a fastening element 41, and the shaft 41 is carried in a bearing 41:: in the center of block 30. A pulley wheel 43 mounted on the outer end of shaft 41 affords means for rotating scanning disc 49 at the appropriate speed. The surface 40a of scanning disc 40 is provided with an opaque coating which has scanning slots, as slots 23 of FIG. 3, formed therein, as will be discussed in more detail later. 'Where, as here, the mask and scan plates are each formed of transparent material with an opaque coating on one surface, it is important that the coated surfaces are positioned closely adjacent each other, to reduce undesired tonal effects of nonparallel light rays which may pass through the mask plate. As bearing 41a is mounted in resilient block 30 In an instrument havingundesired vibration in the motion of the scanning disc is damped, at least in part.

A generator cover member 42' has a shoulder 42a which engages the peripheral surface of mask plate 36, the cover being secured to block 34 by clamp 44 in turn holding the mask plate in position thereon. Extending through an opening 45 in the center of cover 42' is a photosensitive device or photocell tube as, which receives the scanned light that passes through the mask and scanning disc, and converts it to a corresponding elec trical signal. The cover 42' is generally parabolic in shape, and the photosensitive surface of pickup element 46 is positioned substantially at the focal point of the reflector. Cover 42' serves the dual functions of excluding ambient light from the generator, and reflecting light from lamps 35 to the photocell 46, increasing the sensitivity and power output of the generator. Surrounding the base of photocell 46 is a ring 47 of compressible opaque material, as sponge rubber, which prevents the entry of ambient light through the space between the photocell and the cover.

The tone representing areas for the lowest frequency notes, which are found in the first row adjacent the center of block 39, are relatively large in size. In order to provide adequate collimated lighting for these areas, a second lens 48, in addition to the lens 39 integral with the mask plate 36, is provided in the hole 33 through the block. This lens is seated on the shoulder 49 in hole 33 and secured in place by a clamping ring 50.

In the preferred embodiment of the invention, twelve identical tone generators are utilized, one for each note of the octave, and they are arranged generally as shown in FIG. 5, to be driven by a single motor 55 through belt drive 56, connected directly with one of the generators 29. A continuous belt 57 drives the other eleven generators through pulley wheels, as 43 of FIG. 4. Each of the pulley wheels has slightly different diameter to rotate the scanning discs at the appropriate speeds to produce the desired notes. be adjusted by moving idler wheel 58.

Turning now to FIGS. 6 and 7, it is seen that the tone representing areas of mask 36 and the scanning slots of scanning disc 40 are divided into seven groups or rows each having a generally annular arrangement about the center of the mask and scanning plates. In the embodiment of the invention illustrated here, the number of scanning slots is doubled in each succeeding row outwardly from the center. Thus, the scanning speed or rate is doubled in each succeeding row, and each row corresponds to a different octave.

The design of the one generator illustrated herein involves a compromises of several variables which contribute to the quality of the system. It is necessary that each of the note representing, light-transmitting areas of the mask be illuminated uniformly. Thus, the size of the lamps 35 which may be accommodated in the holes 33 in block 30, and the size of the lens systems which may be used therewith determine the maximum size of the mask openings formed in the inner roW 50 of mask 36. The circumferential length or extent of each of the openings must be an integral fraction of the circumference of the row so that it is equal to the spacing between scanning slots in the inner row 64 of scanning disc 40. In the embodiment illustrated, there are nine scanning slots in the first row with an angular spacing of 40 between slots. Thus, the angular extent of each of the mask patterns in the first row, 50, is 40". The notes provided in the first row 50 of the mask represent those notes appearing in the lowest octave of the instrument. The number of scanning slots is doubled in each succeeding row of scanning disc 40 so that the second row 61 has eighteen slots, the third row 62 has the thirty-six slots, the fourth row 63 has seventy-two slots, the fifth row 64 has one hundred and forty-four slots, the sixth row 65 has tWo hundred and eighty-eight slots and the seventh row 66 has five hundred and seventy-six slots. In the corresponding rows The tension in drive belt 57 may quantity decreases as the slot size is decreased.

52-56 of the mask plate, the basic tone patterns each have a longitudinal or circumferential extent equal-to the spacing betweenthe scanning slots.

It can be demonstrated mathematically that if the slot width is equal to the slot pitch or distance between slot centers divided by a number n, it is impossible to reproduce the nth harmonic of the tone pattern scanned. In addition, the sensitivity of the system drops off rapidly as the nth harmonic is approached. Accordingly, the slot width must be chosen so that n is sufliciently large that no significant harmonic is eliminated.

Stated another way, for maximum fidelity, the slot Width must be small in comparison with the slot pitch. However, the amplitude of the signal voltage generated in the photocell is directly related to the quantity of light shining on the sensitive surface of the photocell, and this In the inner rows, the slot width is large enough to pass adequate light even with a relatively large n factor, as of the order of twelve. In the outer rows, the slot width is small and it is necessary that n be reduced. However, the higher harmonics of the relatively high pitch tones of the outer rows are on the fringe of the audible range, and the quality of the generated tones is not significantly impaired by the loss of higher harmonics.

FIG. 8 illustrates the relation of a mask pattern 67 in the first mask row 50, and the associated scanning slots 68 and 69 in the first scanning disc row '69. It will be noted that the longitudinal or circumferential extent of the mask pattern 67 is equal to the pitch or spacing between adjacent scanning slots 63 and 6%, so that one slot starts a scan of the pattern as another finishes. The radial extent of pattern 67 is, of course, less than the radial extent of the scanning slots, so that all the light from the mask pattern is scanned.

It is seen in PEG. 8 that the lagging scanning slot, for example 68, begins scanning of the pattern 67 before the leading slot finishes scanning. it is therefore advantageous to present to the slots, patterns which have ends tapering to points, thereby affording more faithful reproduction of the desired tone qualities especially in the lower and intermediate octaves.

Also, t e pattern s7 is symmetrical above and below its imaginary central circumferential line illustrated in FIG. 8. This has been found particularly advantageous in permitting the use of patterns with a greater radial dimension to pass more light without introducing distortion. This substantially improves the signal-to-noise ratio.

As the slot width decreases in the outer rows (even though the ratio of pitch to width is smaller) the amplitude of the scanned light falling on the photocell decreases, resulting in a reduced signal in the electrical amplifier circuits. This is, of course, undesirable. Accordingly, certain of the mask patterns, beginning in the fourth row 53, are doubled, as best seen in FIG. 9, so that two identical mask patterns as 7% and 71, are scanned simultaneously by slots 72 and 73 in the fourth row of the scanning disc. The longitudinal extent of each of the tone patterns itl and 71 is equal to the pitch between slots 72 and 73 so that the two patterns are scanned exactly simultaneously and the light output to the photocell is doubled. in the fifth row (FIG. 10), three tone patterns 75, 76 and 77 are scanned simultaneously'by slots 78, 7E and hit. This method of increasing the amplitude of the scanned li ht directed on the photocell 'is also utilized in the seventh row as illustrated in H6. 11. Here, four identical tone patterns 31, 82, 8'3

and E54 are scanned simultaneously by slots 85, 86, .87

and 38.

The tone representing areas illustrated in FIGS. 9, l0 and 11, represent the flute notes in the respective rows. It will be noted that the mask areas for the notes in the seventh row, FIG. 11, arediarnond-shaped while those for the lower octaves are rather irregular in configuration. The frequencies in the seventh row are such that eighth row harmonic 56b.

. 8 only the lower order harmonics need be considered, and accordingly the maskpatterns are much simpler than the lower frequencies.

A normal organ requires certain types of tones, 'as those of the flute, in octaves beyond the seven provided by the seven row scanning system illustrated. Accordingly, a frequency multiplying technique is utilized in the seventh row to provide the eighth and ninth octave flute notes. FIG. 12 illustrates a frequency doubling arrangement in which there are two tone representing patterns 99 and 91 having a longitudinal extent equal to the pitch between adjacent scanning lines 92 and 93. Thus, as scanning slot 92 passes over tone patterns and '91, two cycles of the note are produced. Three identical tone patterns are scanned simultaneously to provide the desired amplitude.

This technique is also utilized to produce the fourth harmonic of the seventh row flute note, corresponding with a ninth row flute note, as shown in FIG. 13. Here, there are four identical mask patterns 95, 96, )7 and 98 in the space covered by one pair of scanning slots 92 and 93. In this particular case, four identical tone patterns are scanned simultaneously.

row, as previouslydescribed, are designated 56a and 5a--respectively. ;An examination of tone patterns shows how the family relationship carries through in-the various octaves. The diapason notes are designated by the letter b and occur in each of'the rows, including an The third note in the first row' 50, designated She, represents the sub-bass stop. Harmonics of this note appear in the'seco'nd and third rows at 51c and 52c. The trumpet notes'are designated by the letter d and the lowest note in this stop appears in the second row 51. The equivalent eighth rown'ote for this tone is indicated at 56d in the seventh row. The string notes begin in the second row '51 and are designated by the letter e and appear in the respective rows as 5le-56e. Notes of the dulciana stop are designated by the letter 1'', again beginning'in the second row 53. The remaining notes, indicated by the letter g and occurring in the second through 'fifth rows, represent of the related families of'notes are substantially increased from row to row outwardly to provide the amplitude equalization of the tone signals applied to the .photo cell. Some families of notes are generally sounded with substantially louder intensities than other families of notes; and, therefore, the advantage which can be obtained by increasing the radial dimensions of the tone pattern openings will 'vary from -families to family of notes. a

For example the ilute notes designated by the row number followed by the letter a and the diapason notes designated by the row number and the letterb are sounded with relatively high intensities and therefore require tone pattern openings with relatively large radial dimensions. As a result, the desired amount of amplitude equalization can be obtained inthe'lower trree octaves by merely increasing the radial dimension of the openings from row to row outwardly; but the remaining four octaves require duplication of the tone pattern openings for simultaneous scanning by the slots in orderto achieve the desired amplitude equalization.

However the dulciana notes are normally sounded at a'substantially lowerintensity level and therefore the dulciananotes'filf of the second octave through the note 56 of the seventh octave are provided with sufiicient amplitude equalization merely by the adjustmentof 'the radial dimension'of the tone pattern openings.

While I have shown and described the preferred embodiment of my invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include within the scope of the invention all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. A tone generator for photoelectric musical instruments and the like comprising a source of light, a tone pattern comprising a mask having a pattern opening therethrough, a photoelectric cell, and a chopping mask having a slot therethrough between said tone pattern and said photoelectric cell, the width of said tone pattern opening to the width of said chopping slot being in the ratio of at least twelve to one.

2. A tone generator for photoelectric musical instruments and the like comprising a source of light, a tone pattern comprising a mask having a pattern opening therethrough, a photoelectric cell, and a chopping masll having a slot therethrough between said tone pattern and said photoelectric cell, the width of said tone pattern opening to the Width of said chopping slot having a minimum ratio in the order of twelve to one.

3. A tone generator for photoelectric musical instruments and the like comprising a source of light, a tone pattern comprising a mask having a pattern opening therethrough, a photoelectric cell, and a rotatable chopping mask having a plurality of equally spaced slots there through between said tone pattern and said photoelectric cell, the width of said tone pattern opening to the width of each of said chopping slots having a minimum ratio in the order of twelve to one.

4. A tone generator for producing a plurality of octavely related tone signals in a photoelectric musical instrument comprising a stationary mask having a plurality of tone pattern openings therethrough arranged in rows with respective rows having ditfering numbers of openings, means adjacent one side of the mask for lighting the openings, photosensitive means on the other side of the mask, and a chopping mask adjacent the stationary mask and having a row of equally spaced slots movable past each row of openings, the number of slots being doubled in each succeeding row in one direction, the length of the openings being equal to the distance between opposed slot centers, the Width of the slots being progressively smaller from row to row in said direction and the ratio of the .width of each mask opening to the width of its corresponding slots being greater than the number of the highest significant harmonic in the opening to be reproduced.

5. The combination called for in claim 4 in which the ratio of mask opening width to slot Width is less for the slot row having the most slots than it is for at least some of the slow rows having a lesser number of slots.

6. A tone generating arrangement comprising a plurality of identical discs each having a plurality of light passageways arranged in concentric circles with each row comprising a series of passageways adapted to pass light in a respective difierent pattern with the number of said passageways differing from circle to circle in accordance with the radial dimension of the respective circle for enabling the generation of harmonically related tones responsive to light passing through a passageway of similar pattern in each circle, and a rotatable scanning mask for each disc, each mask having a plurality of light passageways arranged in concentric circles and spaced apart by a distance in each circle corresponding to the angle traversed by a passageway in a respective circle on a respective disc, and means for rotating said scanning masks at difierent rates for traversing the passageways on a respective disc at a rate corresponding to a respective pitch.

7. A tone generator for producing a plurality of octavely related tone signals in a photoelectric musical instrument comprising a stationary mask having a plurality of arcuate tone pattern openings therethrough arranged in radially spaced positions and corresponding to a family of octavely related notes, a source of light for each opening adjacent one side of the mask, a photocell on the other side of the mask, a chopping mask rotatable adjacent the stationary mask and having a circular row of equally spaced radial slots opposite each opening, the number of slots being doubled in each succeeding row outwardly, the Width of the slots being progressively smaller from row to row outwardly and the ratio of the width of each mask opening to the width of its corresponding slots being greater than the number of the highest significant harmonic in the opening to be reproduced, and means focusing the light from the sources onto the photocell, the angles formed by the openings and by the centers of the opposed slots being equal and the radial dimensions of the openings being increased from row to row outwardly to improve the amplitude equalization of the scanned light.

8. A tone generator for producing a plurality of oc tavely related tone signals in a photoelectric musical instrument comprising a stationary mask having a plurality of tone pattern openings therethrough arranged in rows With respective rows having differing numbers of openings, means adjacent one side of the mask for lighting the openings, photosensitive means on the other side of the mask, and a chopping mask adjacent the stationary mask and having a row of equally spaced slots movable past each row of openings, the number of slots being doubled in each succeeding row in one direction, the length of the openings being equal to the distance between opposed slot centers, the width of the slots being progressively smaller from row to row in said direction and the ratio of the width of each mask opening to the Width of its corresponding slots being greater than the number of the highest significant harmonic in the opening to be reproduced, and the transverse dimensions of at least certain related mask openings being increased from row to row in said direction to improve the amplitude equalization of the scanned light.

9. A tone generator for producing a plurality of octavely related tone signals in a photoelectric musical instrument comprising a stationary mask having a plurality of tone pattern openings therethrough arranged in rows with respective rows having diflfering numbers of openings, means adjacent one side of the mask for lighting the openings, photosensitive means on the other side of the mask, and a chopping mask adjacent the stationary mask and having a roW of equally spaced slots movable past each row of openings, the number of slots being doubled in each succeeding row in one direction, the length of the openings being equal to the distance between opposed slot centers, the width of the slots in at least certain rows being smaller than the width of the slots in rows having fewer slots, and the transverse dimensions of at least certain related mask openings being increased in those rows opposite slots having smaller widths.

10. A tone generator for producing a plurality of octavely related tone signals in a photoelectric musical instrument comprising a stationary mask having a plurality of tone pattern openings therethrough arranged in rows, means adjacent one side of the mask for lighting the openings, photosensitive means on the other side of the mask, and a chopping mask adjacent the stationary mask and having a row of equally spaced slots movable past each row of openings, the number of slots being doubled in each succeeding row in one direction, the length of the openings being equal to the distance be- I tween opposed slot centers, the width of the slots being progressively smaller from row to row in said direction and the ratio of the width of each mask opening to the width of its corresponding slots being greater than the number of the highest significant harmonic in the opening to be reproduced, at least certain of the shorter mask openings being duplicated for simultaneous in-phase scanning by the slots in the same row to improve the amplitude equalization ofthe tones and to improve the signal-to-noiseratios, the transverse dimensions of at least certain related mask openings being increased from row to row in said direction to improve the amplitude equaliation of the scanned'light.

11. A tone generator for producing a plurality of octavely related tone signals in a photoelectric musical instrument .comprising a stationary mask having a plurality of tone pattern openings therethrough arranged in concentric circular rows, a source of light for each opening adjacent one side of the mask, a photocell on the other side of the mask, a chopping mask rotatable adjacent the stationary mask and having a circular row of equally spaced radial slots opposite each row of openings, the number of slots being doubled in each succeeding row outwardly, the angles formed between the slots in eachrow being equal to the angle traversed by the openings in a respective row, the width of the slots being progressively smaller from row to row outwardly and the ratio of the width of each mask opening to the width of its corresponding slots being greater than the number ofthe highest significantharmonic in the opening to be reproduced, and means focusing the light from the sources onto the photocell.

12. The tone generator claimed in claim 11 in which the tone pattern openings are radialiy symmetrical on ither sideof a centralarc.

13. The tone generator claimed in claim v 11 in which the ratio of the width of the mask openings to'the width instrument comprising a stationary mask having a plurality of tone pattern openings therethrough arranged in concentriccircular rows, a source oflight for each opening adjacent one side of the mask, a photocell on the otherside ot'the mask, a chopping mask rotatable adjacent the stationary mask and having a circular row of equally spaced radial slots opposite each row of openings, the number of slots being doubled in each succeeding row outwardly, the angles formed by the openings and by the centers of the opposedslots being equal, the width of the slots in at least some of the rows being smaller than the width of the slots in rows inwardly therefrom and the ratio of the width ofeach mask opening to the width of its corresponding slots being greater than the number of the highest significant harmonic in the opening-to-be reproduced, and means focusing the light from the sources onto the photocell.

15. A tone generator for producing a plurality of octavely related tone signalsin a photoelectric musical instrument comprising a stationary mask having a plurality of tone 1 pattern openings therethrough arranged in concentric circular rows, a source of light for each opening adjacent one side of the mask, a photocell on the other side of the mask, a chopping mask rotatable adjacent the stationary mask and having a circular row of equally spaced radial slots opposite each row of openings, the number of slots being doubled in each succeeding row outwardly, he angles formed by the openings and by the centers of the opposed slots being equal, the width of the slots being progressively smaller from row to row outwardly and the ratio of the width of each mask opening to the Width of its corresponding slots being greater than the number of the highest significant hartheme in the opening to be reproduced, the outer rows of mask openings for at least certain tones being duplicated in the same row for simultaneous in-phase scanning by the slots to improve the amplitudes-equalization of the tones and to improve the signal-to-noise ratios, and means focusing the light from the sources onto the photocell.

16. A tone generator for producing a plurality of octavely related tone signals in a photoelectric musical instrument comprising a stationary mask having a plurality of tone pattern openings therethrough arranged in concentric circular rows, a source of light for each opening adjacent one side of the mask, a photocell on the other side of the mask, a chopping mask rotatable adjacent the stationary mask and having a circular row of equally spaced radial slots opposite each row of openings, the number of slots being doubled in each succeeding row outwardly, the angles formed by the openings and by the centers of the opposed slots being'equal, the width of the slots being progressively smaller from row to row outwardly and the ratio of the width of eachmask opening to the width of its corresponding slots being greater than the number of the highest significant harmonic in the opening to be reproduced, the outerrows of mask openings for at least certain tones being duplicated in the same rowfor'sirnultaneous in-phase scanning by the slots to improve the amplitude equalization of the tones and to improve the signal-to-noise ratios, and means focusing the light fromthesources onto the photocell, theradial dimensions of at least certain related mask openings beingincreasedfrom row to row outwardly to improve the amplitude equalization of the scanned'light.

17. A. photoelectric tone generating arrangement comprising a group of light passageways arranged in a pluralityof rows for enabling'the passage of light to a photocell, said passageways arranged so that a different plurality of passageways'is'provided in respective-rows, and a scanning mask having a plurality'of rows of light passageways therein with each row of the latter passageways adapted to traverse arespective row of saidfirst passageways in a sequence wherein a plurality of said group of passageways in one row are scanned simultaneously with only one passageway of said group in another row.

18. The arrangement claimed in claim 17 'in which said group of'passageways is arranged 'with'each row being disposed along a respective .concentriccircle and the shape of one passageway in each circle ditlersfrom'the shape of another'passageway in the respectivecircle.

19. The arrangement claimed in claim 18, in which said group of passageways is provided with tapered ends.

20. The arrangement claimed in claim l7-in which the passageways in a respective row of said scanning mask are spaced apart by a distance corresponding to thelongitudinal dimension of the passageways of said group in a respective row. r

21. The arrangement claimed in claim 17 in which the ratio of the area of said scanning mask passageways in a respective rowto the portion of said scanning disc between passageways in a-respective row is diilerent from row to row.

References 'Cited in the file of this patent UN1T1 .D STATES PATENTS France Feb. 8, 

17. A PHOTOELECTRIC TONE GENERATING ARRANGEMENT COMPRISING A GROUP OF LIGHT PASSAGEWAYS ARRANGED IN A PLURALITY OF ROWS FOR ENABLING THE PASSAGE OF LIGHT TO A PHOTOCELL, SAID PASSAGEWAYS ARRANGED SO THAT A DIFFERENT PLURALITY OF PASSAGEWAYS IS PROVIDED IN RESPECTIVE ROWS, AND A SCANNING MASK HAVING A PLURALITY OF ROWS OF LIGHT PASSAGEWAYS THEREIN WITH EACH ROW OF THE LATTER PASSAGEWAYS ADAPTED TO TRAVERSE A RESPECTIVE ROW OF SAID FIRST PASSAGEWAYS IN A SEQUENCE WHEREIN A PLURALITY OF SAID GROUP OF PASSAGEWAYS IN ONE ROW ARE SCANNED SIMULTANEOUSLY WITH ONLY ONE PASSAGEWAY OF SAID GROUP IN ANOTHER ROW. 